Telephone switching system with programmed auxiliary
control for providing special services

ABSTRACT

1. A TELEPHONE SWITCHING SYSTEM COMPRISING: (A) TRANSMISSION PATHS; (B) FIRST SWITCHING MEANS FOR INTERCONNECTING THE TRANMISSION PATHS; (C) A COMMON CONTROLLING MEANS CONNECTED TO THE SWITCHING MEANS FOR CONTROLLING THE OPERATION OF THE SWITCHING MEANS; AND (D) PROGRAMMED CONTROLLING MEANS CONNECTED TO AND ACTING IN CONSORT WITH THE COMMON CONTROLLING MEANS, FOR MODIFYING THE SEQUENCE OF OPERATION THEREOF IN A PROGRAM RESPONSIVE MANNER, IN RESPONSE TO A REQUEST BY THE COMMON CONTROLLING MEANS FOR SUCH CONNECTION, UPON RECOGNITION BY THE COMMON CONTROLLING MEANS OF ITS INABILITY TO PROCESS A REQUEST FOR SERVICE FROM ONE OF THE TRANSMISSION PATHS WITHOUT SUCH CONNECTION.

5 F. J. SINGER Re. 28,337 F.b I. T BLEPHONE SWITCHING SYSTEM WITH PROGRAMME!) AUXILIARY CQN'ZROL FOR PROVIDING SPECIAL SERVICES Original. Filed Sept. 21, 196'? 15 Sheets-Shea. 1

COMMON CONTROLLING MEANS PROGRAMME!) CONTROLLING -|-5 MEANS FIG. I

FIG 4 FIG 5 FIG. 2

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TBLEPHQNE SWITCHING SYSTEM WITH PROGRAMME!) AUXI CONTROL FOR PROVIDING SPECIAL SERVICES Original Filed Sept. 21, 1967 15 Sheets-Sheet 5 H mo T: l .1.

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TELEPHONE swz-rcmuu sxszau WITH PROGRAMME!) AUXILIARY coumoz. FOR PROVIDING SPECIAL saavrcss Original Filed Sapt. 21, 1967 15 Shasta-Sheet 10 55 405:8 v.23 10.5 53 m F65 mam 55 TN. 25 23m m N mam 5E r H H H H ./L None 1% H M H H 600 C6 C6 .1 C6 C6 It uz: l M2: M2: wzz 96 ]K w .56 WV W g m m J my: w J 1 x5 7 mzfiz v! 3 z. 3.1 1-? wfifi --\mo Ezwuzou" u n n 9m: Efim li 9m: Efim m- 9&6 -55 $5 .55 & i orm; PG m NTCw m Re. 28,337 MED AUXILIARY CBS 1975 F. J. SINGER TELEPHONE SWITCEINQ SYSTEM WITH PROGRAM CONTROL FOR PROVIDING SPECIAL SBRVI Ol'iflilSBl Filed Sept. 21. 1967 15 Sheets-Shoat l 1 m 6 T- 1 86 1 mohmzzou 023 256 n 9-.. PDQ: r J r020 88 i J m5z 55 20E. 3N 0a \1 93 35:: -Il... -l L 5232. n 0234455 L H I I xw fiwn mw 03 n. .2 1 Ski $8 88 555 F r u 25 n n TL- fillfl. VEO 4 r.-|| ||L .58 5th r S E 5356 u 5E v T 182 a |1|| 2-: r 050 u f f 52 625: 198228 05 53:: E; 5&3 0233206 1 ESE. .SQSO 19.5245 M Etna 4 v 5E4: .L 5-

Re. 28,337 XILIAHY Feb. 11, 1975 F. J. SINGER NE SWITCHING SYSTEH WITH PROGRAMMBD AU TELEIHO CONTROL FOR PROVIDING SPECIAL SERVICES Oriana]. Filed Sept. 21, 1967 15 Sheets$heet 14 muhmawm wmohw umohm sl v32. I .llv m .1 m2:

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Original Filed Sept. 21, 1967 United States Patent Re. 28,337 Reissued Feb. 11, 1975 TELEPHONE SWITCHING SYSTEM WITH PRO- GRAMMED AUXILIARY CONTROL FOR PRO- \'lDl.\'G SPECIAL SERVICES Fred J. Singer, Chatham, N.J., assignor to Northern Telecom Inc., Boston, Mass.

Original No. 3,555,196, dated Jan. 12, 1971, Ser. No. 669,436, Sept. 21, 1967. Application for reissue Feb. 22, 197-1, Scr. No. 444.785

Int. Cl. H04q 3/54 11.5. Cl. 179-18 ES 33 Claims Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE A wired logic common control telephone system which has a program controlled auxiliary control system or central programmed control unit operating in consort therewith for particular calls, in order that special features and Centrex operation can be provided to subscribers. For certain call features. interface to the program controlled control unit is made from the marker via a number group connector upon designation of a particular class of service; for others a special circuit which splits a certain type of junctor provides access to an auxiliary interline switching means which is controlled by the program controlled control system, and is activated by a signal from the subscriber whose line is terminated on the common control system. For Centrex operation, a private branch exchange or a remote switching unit is terminated via trunk circuits on a line-link frame in the common control system, and is controlled by the main oflice program controlled control system.

This invention relates to a telephone switching system which utilizes a wired logic common control type of switching system for normal interconnection of subscribers, in combination with a programmed logic applique system operated in consort therewith when certain predesignated types of special telephone calls available to predetermined subscribers are to be setup.

There are in common use today three general types of telephone switching systems. The first type of system is pulse actuated, whereby a transmission path through the switching system is selected as pulses are generated in a subscriber's station set. The most common system of this type uses the well known Strowger switch in step-by-step system.

The second type of switching system utilizes a controlling means in common for all transmission path switching within the system, which operates after all the dialing pulses (rather than each pulse) are received from a subscriber's station set, to find an idle path from the dialing subscribers line circuit to a trunk or to another subscribers line cricuit. This type of system, although much more economical and versatile in its use of controlling equipment with respect to switching equipment, utilizes wired logic for direction of the common control. When one or more subscribers require additional nonstandard features, for instance the ability to initiate a conference call, extensive wiring changes must be made to the common control. Such changes have been found to be expensive and complex, and as the number of changes increases, the probability of connection errors also increases.

The third type of telephone switching system utilizes a common control, but contains a readily changeable operation program which directs a central controller in its performance of switching supervision duties. This type of systern has evolved utilizing electronic techniques and time division operation rather than space division operation and indeed. the central common control has many similarities to modern special-purpose digital computers. It will be referred to herein as a program controlled system. The provision of additional features or changes to a particular subscriber's line is easily effected with this type of system by simply changing the program, which is stored in a memory in the central control. Two general types of these systems have evolved, one for large city central switching offices, and another economical for use in private branch exchanges (referred to below as a PBX). A typical system of the latter type is disclosed in US. Pat. No. 3,225,144 to R. C. Gebhardt et al. issued Dec. 21, 1965, and Bell Laboratories Record, Feburary 1963, p 43; December 1963, p 425; February 1964, p. 61; and November 1964, p. 374.

Telephone switching offices often have a lifetime of 20 to 40 years. It is evident that to replace a recently installed common control telephone switching system by an electronic program controlled telephone switching system to provide services and features not feasible with the common control system may often prove uneconomical and, in fact, may result in financial loss. Thus subscribers connected to such a common control switching system may be deprived of the advantageous features provided economically by a program controlled system. It would thus be extremely advantageous if a way were found to facilitate simple addition of program controlled features to a common control system, without incurring the loss caused by the complete dismantling of the common control system in favor of a program controlled system.

I have invented a telephone switching system which allows program control of special types of telephone calls which may be requested by predetermined subscribers on a common control system. This telephone switching system comprises a first transmission path, a second transmission path, switching means interconnecting the first and second transmission paths, 3 common controlling means for causing the interconnection of selected ones of the first and second transmission paths, and a programmed controlling means connected to the common controlling means for modifying the operation of the common controlling means in response to the reception of predetermined signals received over predetermined ones of the first transmission paths. Thus it may be seen that the prgyision of spcci al features for the system is taken over by a pro- "EFamTtiedcentral control whose program is readily modifiablefand which operates in consort with the common control'equip mnt of a present central ofiice installation. Generally,' th'e'refore, this invention consists of a telephone switching system comprising a common controlled switching means and a li ue pro ammed controlling means counegtgd to said sivfi chi'rig' eans'dfiring the'processing of'predetermmed typTeE Oftlephone calls for modifying the operation thereof in a predetermined manner, in accordance with certain types of requests for service.

It will become obvious to one skilled in the art, understanding this specification that the techniques involved may be applied to well-known types of common control systems, and that the central programmed controlling means can be built around a general purpose digital computer. However, this description will refer specifically to the common control telephone switching system described in US. Pat. No. 2,585,904 to A. J. Busch, issued Feb. 19, 1952 and to the PBX type of program control system described in US. Pat. No. 3,225,144 to R. C. Gebhardt et al. issu d Dec. 21, 1965.

Detailed descriptions of these well-known systems would obscure the specific inventive system concept described herein, and the reader is referred to the aforementioned patents for details as to their structure. However, where interconnections with those systems are required for this intention, a description will be fully disclosed. In addition, as the imention described herein is a system concept, the details of specific logic gate interconnections, methods of causing cross-bar switches to operate, and certain blocks used in the combination are considered well known by those skilled in the art and will not be described in detail, since to describe the specific structure of these well-known pieces of equipment would also only serve to obscure the system invention described herein.

A better understanding of this invention may be obtained by referring to the figures listed below.

FIG. 1 is a block diagram showing the basic system arrangement of this invention;

FIG. 2 shows pictorially how FIGS. 4 and 5 are to be arranged in order to consider them as a single unified drawing:

FIG. 3 shows pictorially how FIGS. 10, ll, 12, 13, 14, I5 and 16 are to be arranged in order to consider them as single unified drawing;

FIGS. 4 and 5 are two portions of one block diagram showing the basic system invention in more detail than that of FIG. 1:

FIG. 6 is a block diagram of this invention showing only those system components necessary during an abbreviated dialing type of call;

FIG. 7 is a block diagram of this invention showing only those system components necessary during a variable transfer type of call,

FIG. 8 is a block diagram of this invention showing only those system components necessary during connection to a subscriber at a Private Branch Exchange (PBX), and at a remote switching unit;

FIG. 9 is a block diagram of this invention showing only those system components necessary during a dial transfer type of call;

FIGS. 10 to 16 are portions of a detailed block schematic of this invention, fitted according to the mosaic shown in FIG. 3, and

FIG. 17 shows the special service circuit shown in FIGS. 10 and 12 connected to a junctor in detached schematic form.

In this specification, where reference numerals are used relating to new apparatus required by this invention, they are designated by a numeral with no lettered prefix. The numeral will consist of a first digit or digits designating the sheet on which the particular element may be found, followed by a dash and the remainder of the number which designates in numerical order for that sheet the element itself. If. for instance. in FIG. 9 the element 7-23 is referred to, it will be recognized that the element 7-23 is primarily related to, and found on sheet 7.

For numerals having a prefix G (for instance G496). it will be recognized that this numeral relates to the Gebhardt et al. patent, which contains its own numbering system. This example relates to element 406, on page 4 of the drawings of the Gebhardt et a]. patent.

The invention will be described according to the following general arrangement, in the order shown:

INDEX 1. General Description 1.1. Common Control System 1.2. Program Control System 1.3. Interface Equipment 2. General Operation 2.1. Abbreviated Dialing 2.2. Variable Transfer 2.3. Remote Switching Unit 2.4. Dial Transfer 2.5. Add-on 2.6. Conference Connections 3. Detailed Description 4 4. Detailed Operation 4.1. Abbreviated Dialing 4.2. Variable Transfer 4.2.1. Registration of Transfer Information 4.2.". Request for Connection 4.2.3. Registration of Original Line Location Number Remote Switching Unit Dial Transfer Addon 1. GENERAL DESCRIPTION FIG. 1 is a block diagram showing the interrelationship of elements defining the basic concept of this invention. First trtuumiision paths l-l and second tran mission paths l-l a'c interconnected by a suitching means l-3. A common controlling means 1-4 operates at various stages during the processing of a call, causes the interconnection of the first transmission paths 1-l to the second transmi sion paths l-Z. Of cour e it uill be recognized that the first transmission paths can be trunks, subscriber line circuits, data links etc., while the second transmission paths can be similarly designated circuits and may be intended to be connected to other central otfices. A programmed controlling means l5 is connected to, and operates in consort with the common controlling means l-4 under certain predetermined circumstances.

When a normal telephone call or request for switching from a first transmission path ll to a second transmis sion path l-2 is required, the common controlling means 1-4 operates the switching means 13 in a normal manner using its wired logic without requiring the use of programmed controlling means. l-lowewr, hen a first transmission path [-1, to which special services may be offered, requests such a special service call, the common controlling means 1-4 requests the programmed controlling means 1-5 to interpret and act in consort therewith, causing it to modify its normal operation, thus allowing such special call to be placed.

Since the traffic handling requirements for special service calls are substantially less than for the general trafiic in a common control telephone switching system, the programmed controlling means l-S need only be large or fast enough to handle such traffic, and thus only have a fraction of the traffic capacity of the common controlling means 1-4. Furthermore, if the programmed controlling means l-5 is provided with capacity larger than that required by the single common control switching office, it can easily provide service to more than one common control switching office, as well as to one or more remote community, or PBX switching units.

It should be emphasized that since the program controlling means l-S operates in consort with and is connected to the ccmmon controlling means 14, the interconnection of various services to a subscriber is extremely fast, and thus satisfactory to the subscriber. Another known system for providing programmed logic control of Centrex calls and Centrex calls with special services utilizes a technique well known as Iine'link pulsing, which is uneconomical in utilization of equipment, and requires the use of additional trunks and wired circuits within the common control system for each coinciding request and setup of service. The system described herein utilizing a programmed controlling means obviates the need for linelink pulsing.

1.1. Common Control FIGS. 4 and 5 assembled according to the plan shown in FIG. 2, is a more detailed block diagram break down of the invention. A common control telephone switching system is shown which depicts the essential elements of a common control telephone switching system similar to that shown in FIGS. 235 and 236 of the aforementioned A. I. Busch patent. which is well described therein.

First transmission paths l-l, or line circuits, are connected to link frames (LLF), and second transmission paths 1-2. or trunks, are connected to trunk link frames (TLF). lunctors interconnect line link frames with trunk link frames. A typical originating register (ORlG REG) and marker are connected via various connectors (shown grouped for simplicity of explanation) to the line and trunk link frames. The originating register is connected to the marker via a originating register marker connector (ORlG-REG MKR CONN), and a number group (NO GP), which stores the line locations of subscribers lines on the line link frames and classes of service thereof, is connected via a number group connector (NGC) to the marker. All the equipment used in common by the switching system to cause the line and trunk link frames to interconnect the line circuits and trunks properly. is termed common control" equipment, and is described in the aforementioned A. J. Busch patent.

1.2. Central Control memories, and is termed herein program control logic.

Memories connected thereto are a call status store G700, which is a temporary memory for keeping track of what stage in predetermined sequences the status of initiation or processing of call stands, a line and trunk information store G802 connected to the program control logic which keeps track of what the status of the line or trunk requesting or having service is, and a program store G1200, also connected to the program control logic, which is a semipermanent memory which contains the program required for the detailed processing of any predetermined type of call utilizing the central programmed control unit. While the call status store G700 and the line and trunk information store G802 have their contents changed many times during the processing of a cell, the information contained in the program store 61200 remains permanent unless an operator changes it purposefully, for instance to allow the provision of an additional special call feature for a particular subscribers line.

Various controlling means within the central programmed control unit are actuated by the program control logic as a result of directions translated from aforementioned memories input and output ports for data are provided for the program control logic, essentially for supervisory purposes.

1.3. Interface Equipment In the first embodiment of this invention a marker buffer translator 5-1 is connected between controlling means actuated by thhe program control logic in the central program control unit, and the marker and number group connector in the common control system.

A marker bid scanner 5-2 is connected between a number group connector, and a data receiver translator (DRT) 5-3, which is further connected into an appropriate data receiving gate in the program control logic.

The combination of the above-described units allows certain type of special service calls, described below, to be provided to subscribers connected to the common control system. A second embodiment of this invention allows certain other types of special services to be provided subscribers.

As shown in FIG. 4, certain junctors which interconnect a line link frame and trunk link frame are modified so as to incorporate special service circuits 4-1 therein. Since the special service circuits are novel to this invention they are fully desrcibed below. A well-known line concentrator 4-2 such as that described in Bell Laboratories Record, September 1965, page 337, interconnects special service circuits 4-1 with an interline switching means 4-3 which can interconnect talking paths between 6 line circuits 4-4. The line circuits 4-4 are connected to transmission path extending through the line concentrator 4-2 or to trunks 4-5.

The interline switching means 4-3 can be the PBX switching unit fully described in the .iforemcntIoned Gebhardt et al. patent and shown in FlGS. 3 and 4 thereof. transmission paths from the concentrator unit 4-2 and trunk circuits 4-5 terminating as line circuits thereon. A control for the interline switch means 4-3 consisting of a digit and data link control 4-6 generally shown in FIG. 4 of the Gebhardt et al. patent is connected thereto. and is interfaced with the central programmed control unit \ia transmitters such as G418 and G618 and recei-ters G401 and G602. similar to the manner described in the aforementioned Gebha 'dt et al. patent.

A remote switching unit 4-7 external to the above described system combination may also be connected in an advantageous manner. The remote sn itching unit includes an interline switching means, digit and data link control and signaling and data receive and transmitters similar to the PBX switching unit described above. Connected to its signalling and data receivers and transmitters are signalling trunks and data trunks shown in FIG. 4 as data link 4-8 and signalling trunk 4-9. Signalling trunk 4-9 and data link 4-8 are connected through to the programmed control logic in the central programmed control unit similar to the manner described in the Gebhaidt et al. patent.

Shown terminated on the remote switching unit 4-7 is a central office trunk G111, which is connected to one of the line circuits on the line link frame of the common control system, and is controlled from the central programmed control unit via control leads G113.

2. GEN ERAL OPERATION A description of the general operation of this invention will be given with reference to FIGS. 6. 7. 8, and 9, which show the essential elements of FIGS. 4 and 5 relating to each special type of call. In order to facilitate the description, sis special service types of calls will be described:

. abbreviated dialing;

. variable transfer;

. connection of a remote switching unit; dial transfer;

. add-on;

. conference.

2.1 Abbreviated Diailng A description of abbreviated dialing will follow with reference to FIG. 6. Abbreviated dialing allows a subscriber to contact certain preselected other line locations using fewer digits than are normally required. For instance, a subscriber, instead of dialing 828-2761 may dial 1135, where the digits H are a code to the switching oflice designating that an abbreviated number follows, and where two-digit 35 is a predetermined number taking the place of seven-digit 828- 761. The two digit combination provides the customer a capacity of l(] abbreviated dialing numbers. including 10 digits inter area code numbers. Thus an abbreviated number is generally of the form IIXY where XX is a predetermined 7 or 10 digit number. Of course, other codes than It may be utilized.

As is described in the A. J. Bush patent, a subscriber in lifting his handset and releasing his hookswitch initiates a. request for service, and the marker MKR. via various connectors, causes an originating register OR to be connected to the subscriber's line 6-1 via the trunk link frame TLF and line link frame LLF. The line location of the calling line 6-1 is passed from the marker into the originating register, in the normal manner. The orginating register applies dial tone through the line link frame and trunk line frame to the calling subscriber's line. If the calling subscriber then dials a normal number. the call is completed in the normal manner by the common control system. Note that all junctors between the line link frame and trunk link frame are proper complete circuit paths.

Assuming now that the subscriber dials the abbreviated code llXX. the digits and subscriber line location are registered in the originating register. The originating register marker connector then connects a circuit through itself betucen the orginating register and the marker to transfer the calling line location and [call member] called Hulrthur thereto. The marker then seizes a number group connector NGC and number group N6, in the normal manner, so that it can obtain a translation of the called number location corresponding to the called number and the class of service of the calling line from the number group. The number group attempts to translate the IIXX digits. and if the class of service is proper, it gives an indication to the marker that the central programmed control unit must be called into service. if the class of service indicates that the calling subscriber does not have the abbreviated dialing feature, it indicates to the marker that the calling line should be connected to an appropriate trttnk such as one which signals no such number."

The marker then causes the number group to be dropped, and appropriate switches in the number group connector leading to the marker bid scanner -2 (MBS) to be closed. The marker bid scanner 5-2 thus senses that the marker is bidding for service, and identifies the number group connector through which it is bidding. The marker bid scanner 5-2 is connected to a data receiver translator 5-3 (DRT), which transmits the request for service from the identified number group connector into the central programmed control unit, acting similar to the manner described in the aforementioned Gebhardt et al. patent with respect to a response to a request for service over a data link through a data receiver such as G602.

A marker bufi'er translator 5-1 (MBT) under control of the central programmed control unit is then connected to the number group connector from which the bid for service came, in a manner similar to that for connecting an idle signal receiver such as G501 in the aforementioned Gcbhardt et al. patent.

The llXX number and equipment location number of the calling line is then transferred from the marker storage relays through the number group connector into the register buffer translator 5-1 and thence into the central programmed control unit.

The central programmed control unit senses the prefix code 11 and recognizes that it is a request for an abbreviated dialing type of call, and calls into use its corresponding program. The central programmed control unit, after consulting it's memory, translates the XX code into a corresponding called subscriber's number, for instance, having seven digits, and transfers the translated directory number of the called line as well as the calling line location via the [register] marker buffer translator 5-1 into the marker. as if the digits had come from an originating register. The marker drops the connection in the number group connector to the marker bid scanner, and reestablishes the connection to the number group. The number group translates the full called line directory number to its line location.

The marker. in receiving the called line directory number, drops its hold on the number group connector and acts to complete the call in the normal manner as described in the aforementioned A. I. Busch patent. The number group connector thus removes its bid for service on the marker bid scanner 5-2, and the marker buffer translator 5-1 is released from the central programmed control unit, which restores itself, the marker buffer translator 5-1, marker bid scanner 5-2 and data receiver trans lator 5-3 to an idle condition in order to await the next request for service.

2.2. Variable Transfer The sequence of events involving a variable transfer type of call will be explained with reference to FIG. 7. Variable transfer is the special feature which allows a predetermined subscriber to have all incoming calls to his line transferred to a preselected different telephone line than his own. The preselection can be made by the subscriber dialing a special code followed by the telephone number of the line he wishes his calls to be transferred to, which we will refer to here as a remote station. All future incoming calls to his line will be transferred to, and automatically ring, the remote station.

A subscriber having the variable transfer feature, whose line is connected to the common control switching system, may initiate a request for service in the normal manner, i.e. by lifting the telephone handset. Again in the manner described in the aforementioned A. I. Busch patent, an originating register is connected through a trunk link frame, junctor, and line link frame to the calling subscriber's line. Dial tone is then returned to the calling subscriber, indicating to him that he may begin dialing.

If the subscriber wishes that all future incoming calls be transferred to a different subscriber's line, for instance designated by telephone number ABX XXXX, thus utilizing his variable transfer feature, he dials the prefix code 12 (or another prefix code predetermined by the telephone company) followed by ABX XXXX. All dialed digits and the calling line location are stored in the originating register 11-4 in the normal manner, the register having enough capacity for the extra two digits.

In addition to the dialed directory number, the originating register 11-4 obtains a class of service indication from the line location of the called line on the line link frame, which is stored along with the dialed directory number in the usual manner. If the class of service indicates that the calling line does not have provision for variable transfer, the marker 11-1 connects the calling line to a trunk which is a source of tone indicating no such number, and the originating register 11-4 is returned to an idle condition.

However, if the class of service indicates that the calling line does [not] have the variable transfer feature, the marker 11[-4]-1 is seized from the originating register marker connector 11-5, and the marker ll[-4]-I seizes a number group 11-9 through a number group connector 11-10 for translation of the dialed directory number to call line location. The number group translates the 12 code as an indication to the marker that the central programmed control unit must be used. The marker [than] then causes the number group connector switches leading to the number group to be opened, and additional switches leading to the marker bid scanner 5-2 and to a marker buffer translator 5-1 to be closed. The marker bid scanner 5-2, sensing the bid for service, initiates a request for service of the central programmed control unit via the data receiver translator 5-3, in a similar manner to that described earlier. The central programmed control unit connects an idle marker bulfer translator 5-1 to the marker via the number group connector, at which time the 12 ABX XXXX code and calling subscribers line location are transferred via the marker buffer translator 5-1 into the central programmed control unit.

The central programmed control unit stores the remote station number and calling line location in its line information store, then transmits the line location number of the calling line and the directory number of the remote station line via the marker buffer translator S-l into the marker. The marker, assuming that these digits came from the originating register in the normal manner, requests a. translation of the line location of the remote station from the number group and completes the connection between the calling and the remote station line. The number group connector is then released by the marker, and the marker bid scanner 5-2 and marker buffer translator 5-1 are released, allowing the central programmed control unit to regain an idle status.

When the customer at the remote station answers the call, the calling subscriber can advise him that he should accept subsequent transferred calls. This act of initially calling the remote station allows verification that the proper directory code had been dialed.

If the remote station set is busy when the call is attempted, the calling subscriber may subsequently verify the transfer by dialing the i2 ABX XXXX digits repeatedly until he contacts a subscriber at the remote station. However, this procedure will not nullify or change the transfer information contained in the central programmed control unit line formation store. Calls can still be initinted from the transferring telephone station, while all incoming calls will be transferred to the remote station.

Subsequently, if the transferring subscriber wishes to cancel the transfer of incoming calls, he performs a procedure identical to that for initiating the call transfer service, but instead of dialing a remote station directory number, he dials the prefix code 12 followed by his own directory number. The central programmed control unit verifies in the line information store that the dialed XXXX digits correspond to his normally assigned number. The registration of the remote station number in the line information store is then canceled by the control unit acting to restore the binary digit reference in the subscribers line location of the line information store. indicating that when subsequent incoming calls are to be completed, they should be completed to the original subscriber's line. The central programmed control unit then sends the line location number of the calling line and directory number of the called subscriber into the marker via the marker buffer translator 5-1. After translation of the directory number by the number group, the marker receives the line location of the directory number. Since the two locations are identical, and the calling subscriber is off hook and is the same subscriber as the called subscriber, the marker thereupon connects the calling subscribers line to trunk which returns busy signal to the calling subscriber. This indicates to the calling subscriber that the remote station transfer registration has been canceled in the central programmed control unit.

An incoming call to a subscriber's line which has utilized the transfer feature, may originate from any line associated with the common control system, a trunk from another telephone exchange, or from a remote switching unit associated with a line circuit connected to the common control system. The sequence of events involving a call from a trunk connected from another exchange will be described below. A call originating from a subscriber's line proceeds in a generally similar manner, as will be understood by one skilled in the art understanding this invention.

Referring to FIG. 7, assume that an incoming trunk 9-2 has been seized, and has transmitted the code digits ABX XXXX into an incoming register (not shown). The incoming register transfers the received digits to the marker, in a similar manner to an originating register during the initiation of a call. as is described in the aforementioned A. I. Busch patent. The marker is then connected to the number group via the number group connector in order to identify the ringing code of the called subscriber's line and its equipment location. The number group passes information to the marker that the called line is provided with variable transfer service, in the normal manner of identifying particular types of ringing code. In response to the signal that this ringing code, analogous to a pseudo class of service is to be extended, the marker causes the number group connector to be connected in a circuit path to the marker bid scanner 5-2.

The connection of the number group connector to the marker bid scanner appears thereto to be a bid for service. The scanner 5-2 identifies the particular number group connector by its location in its clock controlled time cycle. The data receiver translator 5-3 associated with the marker bid scanner 5-2 translates the bid for service and initiates action by the central programmed control unit.

The central programmed control unit sets up a path to an idle marker buffer translator 5-1 connected to the number group connector which has bid for service.

The marker transmits the directory number and pseudo class of service of the called line through the number group connector into the marker bufier translator 5l. which translates it into a form acceptable to the central programmed control unit. The central programmed control unit, having received the class of service information from the number group that the called line is a line which has a variable transfer feature, searches its memory and finds that the called subscriber has requested completion of the call to a designated remote station. In the manner described in the aforementioned Gebhardt et al. patent. the central programmed control unit effects the translation. The translated remote station directory number of the remote station is transmitted from the marker buffer translator 5-1, into the marker as if it had come from a register through a register marker connector. The number group is used again. and this time translates the remote station directory number into its corres onding line location designation, which is then transferred via the number group connector into the marker as if it had been the translated line location of the originally dialed number.

The marker, in receiving the called line location, proceeds to effect completion of the call in the normal manner. The number group connector is disconnected from the marker, thus dropping the bid for service by the marker bid scanner 5-2, and thus the remainder of the central programmed control unit is returned to an idle condition.

If the subscriber having the variable transfer feature had requested that the incoming calls be transferred to a remote station not terminated on his common control system, but to a remote telephone switching common control system, the translated line location from the central programmed control unit would provide the transferred line location to the marker in the normal manner. The marker, now noticing that the call is to be completed via an outgoing trunk to a remote switching oflice, for instance, possibly using a tandem switching oflice, will initiate completion of the call through the outgoing trunk as described in the aforementioned A. I. Busch patent.

2.3. Connection of a Remote Switching Unit A remote switching unit can be a community switching OifiCC or PBX which homes on a large central switching ofi'tce, usually via trunks terminated in line circuits of the central office. The central office is activated by signals transferred through the trunks; since the line circuits receive digit pulses from the trunks, the activation system is often called line link pulsing." The central office is operated as if the call had originated from a subscriber's line circuit terminated on a line link frame. A subscriber terminated on the remote switching office, however, must wait until his initially dialed digits are pulsed a second time over the trunks into the central office if he wishes to communicate with a subscriber not directly connected to the remote switching office. Such a system is described in the aforementioned Gebhardt et al. patent.

Similarly, a subscriber whose line is terminated on a central switching office and wishes to communicate with a subscriber terminated on a remote switching unit such as that described in the Gebhardt et al. patent must dial the digits, then wait until the central switching office connects to the remote switching unit, whereupon the digits are again pulsed thereto over a trunk. Again, a delay in connection of the call is incurred.

In this invention, a transmission path may be set up to a remote switching unit from a line or trunk terminated on the central office and a called subscribers line seized without the requirement of line link pulsing. In fact, the operation of the equipment appears to the calling subscriber to be similar to that which would be observed had the called subscriber's line [been connected to the remote 

